Carbon particles containing graphene crystals are used as materials to constitute secondary batteries, electric double layer capacitors and the like. Graphite particles may typically be graphene-containing carbon particles. The technical references relating to graphene-containing carbon particles may include Patent documents 1 and 2 and Non-patent document 1.
Patent document 1: Japanese Patent Application Laid-open No. 2004-178819
Patent document 2: Japanese Patent Application Laid-open No. 2007-320841
Non-patent document 1: Ki, Chul Park, Seong-Yun Kim, Hitoshi Yamazaki, Hiroshi Tomiyasu, Production of carbon soot in subcritical and supercritical water, 6th Conference on supercritical fluids and their applications, Sep. 9-12, 2001